Fuel cells utilize the chemical reaction of a fuel with oxygen to form water in order to generate electrical energy. For this purpose, fuel cells contain as a key component the so-called membrane electrode assembly (MEA), which is a structure made up of an ion-conducting (usually proton-conducting) membrane and a catalytic electrode (anode and cathode) respectively situated on each side of the membrane. The anode and cathode generally include supported noble metals, in particular platinum. In addition, gas diffusion layers (GDL) may be situated on both sides of the membrane electrode assembly, on the sides of the electrodes facing away from the membrane. The fuel cell is generally formed by a plurality of MEAs situated in the stack whose electrical power is additive. Bipolar plates (also referred to as flow field or separator plates), which ensure that the single cells are supplied with the operating media, i.e., the reactants, and which are often also used for cooling, are generally situated between the individual membrane electrode assemblies. In addition, the bipolar plates ensure an electrically conductive contact with the membrane electrode assemblies.
During operation of the fuel cell, the fuel (anode operating medium), in particular hydrogen H2 or a hydrogen-containing gas mixture, is supplied to the anode via a flow field, open on the anode side, of the bipolar plate, where an electrochemical oxidation of (H2) to form protons (H+) takes place with release of electrons (H2→2 H++2 e−). (Water-bound or water-free) transport of the protons from the anode chamber into the cathode chamber takes place via the electrolyte or the membrane which separates in a gas-tight manner and electrically insulates the reaction chambers from one another. The electrons provided at the anode are supplied to the cathode via an electrical line. The cathode is supplied with oxygen or an oxygen-containing gas mixture (air, for example) as cathode operating medium via a flow field of the bipolar plate which is open on the cathode side, so that a reduction of O2 to O2− takes place with acceptance of the electrons (½ O2+2 e→O2−). At the same time, in the cathode chamber the oxygen anions react with the protons which are transported across the membrane, forming water (O2−+2 H 4 H2O).
To ensure the ion conductivity of the electrolytes or the membranes of the MEA, they must generally be constantly moistened. For this purpose, a humidifier is integrated into an anode/cathode exhaust gas path and into an anode/cathode supply path of the fuel cell in order to withdraw moisture from the water-containing fuel cell exhaust gases and supply this moisture to the freshly supplied operating media. Water vapor-permeable membranes which allow transfer of moisture but prevent mixing of the exhaust gases with the fresh operating media are generally used for this purpose.
The anode/cathode exhaust gas path of the fuel cell system may also include a turbine in order to recover energy, for example for driving a compressor in the anode/cathode supply path, by expansion of the exhaust gases. This turbine may be damaged by liquid water contained in the exhaust gas or by condensate formation. For this reason, the turbine is generally situated in the exhaust gas line downstream from the humidifier and optionally downstream from additional water separators. Various relative configurations of the humidifier and water separators are known from the prior art.
DE 10 2004 022 245 A1 and DE 10 2004 022 312 A1 describe a moisture exchange module which includes a bundle of hollow fiber membranes that are permeable to moisture, and a supply line for a gas stream which flows through the hollow fiber membranes, means for separating liquid particles in the gas flow being provided in the area between the supply line and the membrane bundle.
WO 2013/026514 A1 and DE 10 2012 018 863 A1 describe a gas/gas humidification device through which an operating medium stream, which flows to a fuel cell, and an exhaust gas stream, which flows from the fuel cell, flow, and which are separated by a water vapor-permeable membrane inside the humidification device. The gas/gas humidification device also includes an integrated water separator which is integrated downstream from the membranes in the flow direction of the moist exhaust gases.
U.S. Pat. No. 6,953,635 B2 describes a humidifier for a fuel cell which includes a plurality of water vapor-permeable hollow fiber membranes situated in a housing, through which a moist fuel cell exhaust gas flows and around which a dry fuel cell operating gas flows. The housing includes integrated water separators that are situated in a supply line area of the exhaust gas and/or in a discharge area of the operating gas.